What are wildcards in SQL?

Wildcards in SQL are special characters used with the LIKE operator to perform pattern matching and flexible searches.

In simple words:

Wildcards help search partial text instead of exact values.

Why Wildcards are Important

Enterprise applications frequently require:

• Partial searches
• Search suggestions
• Flexible filtering
• Pattern matching
• User-friendly search functionality

Wildcards help:

• Search incomplete data
• Implement dynamic filtering
• Improve search experience

Simple Real-Life Example

Think about:

• Searching employee names starting with "N"

Without Wildcards

WHERE employee_name = 'Naresh'

Matches only:

Naresh

With Wildcards

WHERE employee_name LIKE 'N%'

Matches:

Naresh
Nikhil
Naveen

Wildcards Internal Architecture

Read Column Value
        |
        v
Apply Wildcard Pattern
        |
        v
Pattern Match?
     /           \
   Yes             No
    |               |
Return Row       Ignore Row

Main Wildcards in SQL

1. % Wildcard

The % wildcard represents:

• Zero or more characters

Employees Table Example

Example: Starts With N

SELECT employee_name

FROM employees

WHERE employee_name LIKE 'N%';

Result

Naresh
Nikhil
Naveen

Meaning

Find names:

• Starting with N

Example: Ends With h

SELECT employee_name

FROM employees

WHERE employee_name LIKE '%h';

Result

Naresh
Rahul

Meaning

Find names:

• Ending with h

Example: Contains ar

SELECT employee_name

FROM employees

WHERE employee_name LIKE '%ar%';

Result

Naresh

Meaning

Find names:

• Containing "ar"

2. _ Wildcard

The _ wildcard represents:

• Exactly one character

Example

SELECT employee_name

FROM employees

WHERE employee_name LIKE '_a%';

Meaning

Find names:

• Having "a" as second character

Example Results

Naresh
Rahul

Difference Between % and _

Example Comparison

Using %

LIKE 'N%'

Matches:

N
Na
Naresh
Nikhil

Using _

LIKE 'N_'

Matches:

No
Ne

But NOT:

Naresh

Combining Wildcards

Wildcards can be combined together.

Example

SELECT employee_name

FROM employees

WHERE employee_name LIKE 'N__%';

Meaning

Find names:

• Starting with N
• Having at least 3 characters

Wildcards Query Flow

Read String
      |
      v
Apply Wildcard Rules
      |
      v
Pattern Matches?
 /              \
Yes              No
 |                |
Return Row      Ignore Row

Wildcards with Numbers

Wildcards can also work with:

• Numeric values converted to strings

Example

SELECT *

FROM products

WHERE product_code LIKE '10%';

Purpose

Find product codes:

• Starting with 10

Wildcards with Dates

Wildcards can filter:

• Date patterns

Example

SELECT *

FROM orders

WHERE order_date LIKE '2026-05%';

Purpose

Find orders:

• Placed in May 2026

NOT LIKE with Wildcards

NOT LIKE excludes:

• Matching patterns

Example

SELECT employee_name

FROM employees

WHERE employee_name NOT LIKE 'N%';

Purpose

Retrieve employees:

• Whose names do not start with N

Wildcards and ESCAPE Character

Sometimes:

• Actual % or _ symbols need searching

Example

SELECT *

FROM products

WHERE product_name LIKE '%\%%'
ESCAPE '\';

Purpose

Find product names:

• Containing % symbol

Wildcards vs Regular Expressions

Performance Consideration

Efficient Pattern

LIKE 'N%'

• Can use indexes efficiently

Less Efficient Pattern

LIKE '%ar%'

• May require full table scan

Why?

Leading wildcard:

• Prevents efficient index usage

Optimization Techniques

• Use indexed columns
• Avoid leading wildcards when possible
• Use full-text search for large systems

Real-Time Banking Example

Banking systems use wildcards for:

• Customer searches
• Transaction reference filtering
• Branch code matching

Example

WHERE customer_name LIKE 'Raj%'

Real-Time E-Commerce Example

E-commerce platforms use wildcards for:

• Product searches
• Brand filtering
• Search suggestions

Example

WHERE product_name LIKE '%Laptop%'

Real-Time Learning Platform Example

Learning platforms use wildcards for:

• Course searches
• Technology filtering
• Student lookup systems

Example

WHERE course_title LIKE '%Spring Boot%'

Wildcards in Microservices

Microservices use wildcards for:

• Search APIs
• Autocomplete systems
• Filtering services

Advantages of Wildcards

• Flexible pattern matching
• Simple syntax
• Useful for partial searches

Disadvantages of Wildcards

• Can reduce query performance
• Leading wildcards may trigger full table scans

Best Practices

• Use indexed columns
• Avoid unnecessary leading wildcards
• Use full-text search for large-scale systems
• Optimize frequently searched fields

Common Interview Mistake

Many developers think:

• % and _ behave the same way

Reality

% matches:

• Zero or more characters

while _ matches:

• Exactly one character

Related Learning Topics

• What is LIKE Operator in SQL?
• Difference Between BETWEEN and IN
• What is WHERE Clause in SQL?
• What is an Index in SQL?
• MySQL Performance Optimization

Professional Interview Answer

Wildcards in SQL are special characters used with the LIKE operator for pattern matching and partial text searches. The two main wildcards are % and _. The % wildcard represents zero or more characters, while the _ wildcard represents exactly one character. Wildcards are widely used in search systems, filtering operations, autocomplete functionality, analytics platforms, and dynamic query generation. Enterprise applications such as banking systems, e-commerce platforms, learning management systems, and microservices-based APIs use wildcards extensively for flexible user-friendly searches and filtering operations.

Why Interviewers Like This Answer

• Clearly explains wildcard functionality
• Includes pattern matching concepts
• Shows performance awareness
• Provides enterprise-level examples
• Explains % vs _ differences clearly

Frequently Asked Questions

What are wildcards in SQL?

Wildcards are special characters used for pattern matching in SQL.

What does % mean in SQL?

% represents zero or more characters.

What does _ mean in SQL?

_ represents exactly one character.

Which operator uses wildcards?

Wildcards are mainly used with the LIKE operator.

Why can wildcard searches become slow?

Leading wildcards may prevent efficient index usage and trigger full table scans.